Electrophysiological and haemodynamic effects of vernakalant and flecainide in dyssynchronous canine hearts

About one-third of patients with mild dyssynchronous heart failure suffer from atrial fibrillation (AF). Drugs that convert AF to sinus rhythm may further slowdown ventricular conduction. We aimed to investigate the electrophysiological and haemodynamic effects of vernakalant and flecainide in a canine model of chronic left bundle branch block (LBBB). Left bundle branch block was induced in 12 canines. Four months later, vernakalant or flecainide was administered using a regime, designed to achieve clinically used plasma concentrations of the drugs, n = 6 for each drug. Epicardial electrical contact mapping showed that both drugs uniformly prolonged myocardial conduction time. Vernakalant increased QRS width significantly less than flecainide (17 +/- 13 vs. 34 +/- 15%, respectively). Nevertheless, both drugs equally decreased LVdP/dt(max) by similar to 15%, LVdP/dt(min) by similar to 10%, and left ventricular systolic blood pressure by similar to 5% (P = n.s. between drugs). Vernakalant prolongs ventricular conduction less than flecainide, but both drugs had a similar, moderate negative effect on ventricular contractility and relaxation. Part of these reductions seems to be related to the increase in dyssynchrony.